Equine Embryo Transfer

A small warmblood breeder uses equine embryo transfer to get a foal from her dressage horse.

I had been breeding Oldenburgs and Hanoverians for five years with fresh and frozen semen when, in 2007, I decided to try an equine embryo transfer (ET) with my dressage horse. I felt I was doing equine embryo transfer for all the right reasons: My mare was an upper-level competition dressage horse, and I didn't want to interrupt her training schedule or stretch out her abdominal muscles. My dressage horse was dear to me, and there is always some risk to the dam during labor. She was one of only a handful of mares in the United States by Day Dream, a German Grand Prix dressage competitor who had had relatively few offspring.

Getting Started
All of my breeding work is done by theriogenologists (veterinarians who are board certified specialists in reproduction). It was because of the experience of my theriogenologist, Bill Ley, DVM, that I was willing to undergo the expense of an equine embryo transfer. Here is the basic ET drill:

1. The donor mare is inseminated with a stallion's fresh chilled or frozen semen around the time of ovulation to create an embryo.

2. At 8 days old, the embryo is flushed out of the donor mare's uterus and placed into a suitable surrogate mare that carries the pregnancy to full term.

The first time I tried ET, I opted to use my own surrogate mare. I found a sweet Shire who was in the ideal age range (5 to 10), in good health, had had at least one baby, was bigger than my donor mare and had a good personality.

Synchronize, Breed, Flush, Implant
I gave my mare about three weeks off from serious work during the breeding process and embryo retrieval. Both mares needed to be at the same relative place in their reproductive cycles to increase the chances of the embryo surviving the transfer when that time came. It was a huge cost savings for me to be able to do this at home with the hormone protocol prescribed by Dr. Ley. Every other day, my local veterinarian came out to ultrasound both mares to track their cycles. It was like the race of the tortoise and the hare. One day one mare would be way ahead in her follicular development and the next day the other mare's follicle would jump into the lead.

Finally, it was time to bring my mare to the repro center for breeding (via frozen semen) with the stallion I had chosen for her, San Amour. He had just been awarded the highest dressage index at his stallion test in Germany. I was enthusiastic about the pairing and I only had to wait a little more than a week to find out if I had an embryo rather than the typical 14-day pregnancy check.

Eight days after breeding, we loaded up the big Shire and my more diminutive competition mare and brought them to the vet's farm again. During the "flush" a special fluid was instilled in the donor mare's uterus via catheter and the microscopic embryo, if present, would be captured in a filter. The contents of the filter were examined by the veterinarian under a microscope, and I quickly heard that we had a healthy-looking embryo. It was implanted in the Shire mare and a few minutes later we loaded up to go home.

The next milestones passed by with surprising ease. The Shire mare was pregnant at 14 days, 30 days and 60 days. I could hardly believe my beginner's luck. I settled in for the rest of the almost one-year wait for my dream foal and another I had bred via frozen semen that my other mare would carry herself. I was expecting two foals in April 2008.

Bad Luck
Just about the time I was expecting the birth of my two foals, I was rear-ended by a dump truck and was hospitalized for three weeks. So I arranged to have both mares?due within days of each other?monitored and foaled out at a breeding farm close to my home.

The Shire mare made us wait and wait and finally, one morning when my phone rang, I recognized the number of the breeding farm. The foal had arrived, but there were complications: It was a difficult delivery, the contractions weren't normal and the foal had to be pulled out by the attendants, who had called the vet to assist. Once the colt, a striking black beauty, had been delivered, the Shire mare inexplicably sat down on him and no one could get her up. I had never experienced the heartbreak of breeding before, but here I was with my first foal death. I was devastated but assured that everything was being done for the Shire mare, who obviously needed care now. I was thankful to have my other healthy filly born that year. She was a keeper and special in her own right. In fact, she is currently pregnant with her first foal due in April.

Try Again
I was a little fearful to try ET again, but in 2010 I summoned up my courage as I really wanted a foal from my competition mare. By now, she was trained in all the Grand Prix movements, and I longed to see what she would produce. I did several things differently: I chose a different sire, Stedinger, and I opted to use the repro vet's surrogate mare, Lips.

Just like before, my wonderful mare became pregnant on one dose of frozen semen, but this time, when flushed, she gave us two embryos. I had to decide whether to put one embryo in each of two mares or to put both embryos into one mare to increase the chances of a full-term pregnancy. A third option could have been to freeze one embryo for later implantation and, hindsight being 20/20, I wish I would have gone that route because my mare died in August 2011 during a brief hospitalization.

I opted to put both embryos into the vet's mare and, lo and behold, both pregnancies took. Dr. Ley skillfully pinched one twin, remarking that he
had left me the Olympian.

Happy Ending
Again, the surrogate mare sailed through all of the pregnancy checks, and the foal was fetal-sexed as a colt. One morning about six weeks before the surrogate's due date and before she had developed any udder to speak of, I received a call from my farm manager. He said there was a "surprise" in the stall with Lips, the surrogate mare. I didn't know I could get to the barn so fast, but there he was, a solid black colt with a star. But Lips had no milk.

Fortunately, this colt's birth has a happy ending. He was a little bit of what's referred to as a "dummy foal" and needed some extra veterinary care for the first five days of his life. Dummy foal syndrome (also known as neonatal maladjustment syndrome) is caused by brain swelling or low-oxygen concentrations (hypoxia) in the blood. Dr. Ley said it was possible the colt had had a difficult birth, but since he was born without human assistance, no one really knows for sure.

Since Lips had not developed an udder full of milk, she was given Domperidone to induce lactation, and soon that brought her milk in. The colt was feisty with all the medical interventions he required and the name "Shameless" seemed to suit him. Not wanting to be left out of the excitement, my favorite broodmare delivered her healthy and robust filly within hours of Shameless' arrival. She was much earlier than expected, too, making for a very dramatic few days.

Fast-forward three months: Shameless is inspected by the German Oldenburg Verband/Oldenburg Horse Breeders Society. He seemed to know this was his day to shine, and he proudly trotted around the triangle with Lips, despite the steamy July temperature. At the end of the inspection, Shameless was named a Premium colt and a Foal of Distinction. He was complimented on his lovely type, gaits and conformation. In February 2012, it was announced that Shameless was named the Reserve Champion Oldenburg Colt on the entire North American Tour.

I felt particularly happy that I had persevered to try another embryo transfer with my mare, despite my less-than-happy result the first time around. I'm thrilled that I have Shameless to carry on my competition mare's legacy.

The Cost of Equine Embryo Transfer

William Ley, DVM, explains that the costs associated with application of embryo transfer (ET) depend on multiple factors:

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1. Whether or not the donor mare owner also has his or her own recipient mare or mares available; if not, they will have to either purchase or lease one or more recipient mare for use as surrogate(s).

2. Whether or not an attempt will be made to get more than one or two embryos from the donor mare; this can add anywhere from $500 to $1,000 to the cost of the procedure.

3. The method of breeding the donor mare; frozen-semen breeding is typically more expensive to perform as well as less likely to induce conception when compared to freshly collected and inseminated semen.

4. Whether any cooled-transport or cryopreservation of recovered embryo(s) will be performed.

Minimally, the mare owner can expect to invest at least $1,500 in the ET process per donor breeding cycle with no guarantee for success when a recipient mare is provided. The estimated cost range in the United States is expected to be from $5,000 to $7,500 when a leased recipient mare is used. Quite often the costs can and do overrun the estimate.

Dr. William B. Ley Explains Equine Embryo Transfer

Embryo transfer (ET) is the most widely practiced assisted reproductive technology, and it is not new. The first successful equine embryo transfer was reported in 1972, yet limitations set by breed registries slowed its adoption by mare owners. Mares cannot be as successfully superovulated, adding yet another limiting factor preventing its widespread application. A donor mare under optimal stimulation will produce only two to three embryos per transfer cycle.

The reasons a breeder may want to consider using ET include: 1) obtaining foals from donor mares during their athletic or performance years; 2) getting multiple foals from individual donors during a given season or year; 3) successfully getting foals from young maiden mares, 4) from mares with debilitating health problems and 5) from reproductively unsound mares. ET was initially proposed as a promising method for obtaining foals from aged mares (e.g., late teens to early 20s), but research shows that these embryos have low survival rates.

The donor and surrogate mares should be examined thoroughly prior to their selection and be in good health. A surrogate's optimal age is less than 14 years. Preferably, she should have had at least one prior foal. Synchronizing estrus between donor and recipient mares can be accomplished with hormonal protocols.

Embryo recoveries have been successfully performed from donor mares bred with frozen, extended-cooled transported and freshly collected semen. Regardless of the breeding technique used, it is paramount to pinpoint ovulation time to within a 12-hour window. Embryos are selectively transported through the oviduct into the uterus by day 5 or 6 post-ovulation, at which time they are potentially available for retrieval from the uterus using a simple flushing technique. They can be recovered over the range of day 6 to 9 post-ovulation.

The mare is restrained in stocks, where her perineal area is cleansed with a mild detergent, rinsed and dried. The operator introduces a sterile balloon-tipped catheter, which enters the vagina and is passed through the cervix and into the uterine body. The balloon tip is inflated with sterile saline. The uterus is flushed three to four times with a warm embryo-flushing fluid. The flush fluid flows back out through the catheter and is passed through an embryo-capturing filter. The embryo capture filter cup is examined under a dissecting or stereo microscope. When an embryo is identified, it is "washed," examined and graded for quality. Transfer to the surrogate should take place quickly, as pregnancy rates drop if the embryo is out of the mare for more than one or two hours.

William B. Ley, DVM, MS, DACT, has taught hundreds of veterinarians at the Virginia-Maryland Regional College of Veterinary Medicine and developed the Foal Watch test kit. Author of the book, Broodmare Reproduction, Made Easy for the Equine Practitioner, he runs a private practice in Northern Virginia (vahorsevet.com).

Shari Glickman is a Grade IV Para-equestrian and Oldenburg breeder at her GoodNess Ridge Farm in Mount Airy, Maryland (goodnessridge.com).

The following article originally appeared in the January 2013 issue of Dressage Today magazine. If you enjoyed this article, consider subscribing.

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